Incest always carries the possibility of abuse or exploitation, even between adults. That concerns me more than anything else. I believe it is highly unlikely that anyone could have a psychologically healthy incestuous relationship, because it goes against parent-child and sibling imprintings, but there is very little in human relationships that is impossible.

States have long outlawed incest and consanguinity on public health grounds and will probably continue to do so. The lack of clamor to relax these laws is an indication that there is little interest in recognizing such relationships, and this is very different from the situation with same-sex relationships.

Or maybe you can cite statistics that indicate that you are doing something other than setting up a straw man with your continuing effort to conflate discussion of homosexual relationships with incest?